Syntheses, Spectra, and Structures of (Diphosphine)platinum(II) Carbonate Complexes

Article abstract of DOI:10.1021/ic9603159

A variety of (diphosphine)platinum(II) carbonate complexes, (LL)Pt(CO₃), are readily prepared from the corresponding (diphosphine)platinum dichlorides by treatment with silver carbonate in dichoromethane solution provided that water is present. This reaction also permits facile preparation of analogous ¹³C-labeled complexes. The carbonate ligands in these complexes have been characterized by IR and ¹³C NMR spectroscopy. Alternative preparative routes involve conversion of the precursor dichlorides to the corresponding dialkoxides or diphenoxides, followed by treatment with water and carbon dioxide. Various reaction intermediates have been spectroscopically observed in the latter syntheses. Two crystalline modifications of (Ph₂PCH₂CH₂CH₂PPh ₂)Pt(CO₃), one with and one without a dichloromethane of solvation, have been studied by single-crystal X-ray diffraction. Crystal data for PtP₂O₃C₂₈H₂₆: P2₁/c, Z = 4, T = 200 K, a = 10.362(8) ?, b = 14.743(6) ?, c = 19.183(10) ?, β = 122.69(6)°. Crystal data for PtP₂O₃C₂₈H₂₆·CH ₂Cl₂: P2₁/c, Z = 4, T ≈ 298 K, a = 11.744(2) ?, b = 15.526(3) ?, c = 15.866(3) ?, β = 101.58(1)°.

Full text of DOI:10.1021/ic9603159

5478
Inorg. Chem. 1996, 35, 5478-5483
Syntheses, Spectra, and Structures of (Diphosphine)platinum(II) Carbonate Complexes
Mark A. Andrews,* George L. Gould,† Wim T. Klooster, Kristina S. Koenig,‡ and
Eric J. Voss§
Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
ReceiVed March 22, 1996X
A variety of (diphosphine)platinum(II) carbonate complexes, (LL)Pt(CO3), are readily prepared from the
corresponding (diphosphine)platinum dichlorides by treatment with silver carbonate in dichoromethane solution
provided that water is present. This reaction also permits facile preparation of analogous 13C-labeled complexes.
The carbonate ligands in these complexes have been characterized by IR and 13C NMR spectroscopy. Alternative
preparative routes involve conversion of the precursor dichlorides to the corresponding dialkoxides or diphenoxides,
followed by treatment with water and carbon dioxide. Various reaction intermediates have been spectroscopically
observed in the latter syntheses. Two crystalline modifications of (Ph2PCH2CH2CH2PPh2)Pt(CO3), one with and
one without a dichloromethane of solvation, have been studied by single-crystal X-ray diffraction. Crystal data
for PtP2O3C28H26: P21/c, Z ) 4, T ) 200 K, a ) 10.362(8) Å, b ) 14.743(6) Å, c ) 19.183(10) Å, â )
122.69(6)°. Crystal data for PtP2O3C28H26‚CH2Cl2: P21/c, Z ) 4, T ≈ 298 K, a ) 11.744(2) Å, b ) 15.526(3)
Å, c ) 15.866(3) Å, â ) 101.58(1)°.
spectrum (δ 2.99 (1:2:3:2:1 quintet, JHD ) 1.6 Hz)). Phosphines were
purchased from Strem or Quantum Design. (Diphosphine)platinum-
(II) dichloride complexes were synthesized from K2PtCl4 (caution:
allergen) by the procedure of Slack and Baird8 or from (COD)PtCl2
(COD ) 1,5-cyclooctadiene) according to the procedure of Hackett
and Whitesides.9 In the latter case, it is important to add the phosphine
to the COD complex and to avoid an excess of phosphine in order to
prevent formation of the dicationic complex [(LL)2Pt2+][Cl-]2.10 The
dichloride complexes were optionally recrystallized by slow diffusion
of hexane into a dichloromethane solution to remove traces of water
and/or alcohol. Silver carbonate was prepared from silver nitrate and
sodium carbonate in water, dried under vacuum, and stored protected
from light. Ag213CO3 was purchased from Aldrich. Sodium isopro-
poxide was prepared by reaction in toluene of sodium metal with
isopropyl alcohol that had been dried over sodium isopropoxide.
Sodium p-methoxyphenoxide was prepared by reaction of p-meth-
oxyphenol and sodium hydride in THF, followed by filtration and
precipitation of the product with hexane.
Introduction
(Diphosphine)platinum(II) carbonate complexes, (LL)Pt-
(CO3), are excellent precursors for the preparation of Pt(II)
diolate and alditolate complexes,1 as well as a number of other
(LL)PtIIX2 and (LL)Pt0(L′) compounds.2 They have typically
been synthesized by reaction of the corresponding dichlorides
with silver carbonate3-5 or by treatment of the corresponding
dioxygen complex with carbon dioxide.2,5-7 Difficulties we
encountered in reproducing the former preparations and limita-
tions of the latter approach led us to undertake a more detailed
study. The underlying problem with the silver carbonate route
has been resolved, and additional new synthetic routes have been
developed. The resulting complexes have been characterized
by a variety of physical techniques.
Experimental Section
Typical Silver Carbonate Reaction: Synthesis of (dppp)Pt(CO3).
Solid Ag2CO3 (410 mg, 1.487 mmol, 1.22 equiv) was added to a
solution of (Ph2PCH2CH2CH2PPh2)PtCl2 (825 mg, 1.216 mmol) in a
minimum volume of wet CH2Cl2 (125 mL) without any attempt to
exclude air. The reaction mixture was wrapped with aluminum foil
and stirred for 3 h, at which time a 31P NMR spectrum showed that the
reaction was complete. The solution was filtered through a fine-porosity
frit, and the solids were washed with CH2Cl2 (3 × 5 mL). The filtrate
and washes were then concentrated to approximately 20 mL, and hexane
(20 mL) was added. The resulting white crystalline precipitate was
collected using a fine-porosity frit under slight vacuum and dried under
high vacuum to give pure (dppp)PtCO3 (700 mg, 88% yield), identified
General Procedures. General methods and instrumentation have
been described previously.1 Syntheses and reactions were generally
conducted under argon, but synthetic workups can usually be conducted
in air. Wet dichloromethane was prepared by shaking reagent grade
dichloromethane with water in a separatory funnel and drawing off
the bottom dichloromethane layer into a bottle for storage. Dichlo-
romethane-d2 was vacuum-distilled from calcium hydride. (Note: If
CD2Cl2 is allowed to stand over CaH2 for more than 1 or 2 d, detectable
1
quantities of CHD2Cl form, identified by its characteristic H NMR
† Present address: Department of Chemistry, M/C 111, University of
Illinois, P.O. Box 4348, Chicago, IL 60680.
1
by comparison of 31P and H NMR data with those of an authentic
‡ Present address: Pharmacia & Upjohn Inc., 1500-91-2, Kalamazoo,
MI 49001.
sample.1
§ Present address: Department of Chemistry, Southern Illinois University,
Edwardsville, IL 62026-1652.
The complexes (Ph3P)2Pt(CO3), (dppe)Pt(CO3), (dppb)Pt(CO3),
(dcpe)Pt(CO3), (dtpe)Pt(CO3), (dppv)Pt(CO3), and (dppz)Pt(CO3) were
prepared by a similar procedure, with synthesis times varying from 1
to 24 h. Definitions of phosphine abbreviations, reaction yields, and
spectral data for these complexes are found in Table 1. Details of
syntheses are provided in the Supporting Information.
13C-Labeled Complexes. 13C-labeled platinum carbonate complexes
were prepared analogously by employing Ag213CO3.
X Abstract published in AdVance ACS Abstracts, August 15, 1996.
(1) Andrews, M. A.; Voss, E. J.; Gould, G. L.; Klooster, W. T.; Koetzle,
T. F. J. Am. Chem. Soc. 1994, 116, 5730-5740.
(2) Blake, D. M.; Roundhill, D. M. Inorg. Synth. 1978, 18, 120-124.
(3) Anderson, G. K.; Lumetta, G. J.; Siria, J. W. J. Organomet. Chem.
1992, 434, 253-259.
(4) Goldsworthy, D. H.; Hartley, F. R.; Marshall, G. L.; Murray, S. G.
Inorg. Chem. 1985, 24, 2849-2853.
(5) Hayward, P. J.; Blake, D. M.; Wilkinson, G.; Nyman, C. J. J. Am.
Chem. Soc. 1970, 92, 5873-5878.
(8) Slack, D. A.; Baird, M. C. Inorg. Chim. Acta 1977, 24, 277-280.
(9) Hackett, M.; Whitesides, G. J. Am. Chem. Soc. 1988, 110, 1449-
1462.
(6) Scherer, O. J.; Jungmann, H.; Hussong, K. J. Organomet. Chem. 1983,
247, C1-C4.
(7) Nyman, C. J.; Wymore, C. E.; Wilkinson, G. J. Chem. Soc. A 1968,
561-563.
(10) Cf.: Anderson, G. K.; Davies, J. A.; Schoeck, D. J. Inorg. Chim. Acta
1983, 76, L251-L252.
S0020-1669(96)00315-1 CCC: $12.00 © 1996 American Chemical Society

(Diphosphine)platinum(II) Carbonate Complexes
Inorganic Chemistry, Vol. 35, No. 19, 1996 5479
Table 1. Synthetic and Spectroscopic Data for (LL)Pt(CO3)
Complexes
(major) and δ 2.15 (minor) (about 2.5 ppm upfield of the “triplet” due
to the P-CH2 group of (dppm)Pt(CO3)), as well as a peak at δ -1.42
attributed to a platinum hydride (d, JPH ) 1 Hz (JPtH ) 410 Hz)) whose
area was approximately equal to that of the CH2 group of the minor
product.
synth methodb
(yield/%)
δ (31P)c
(JPtP/Hz)
δ (13CO3)c
(JPtC, JPC/Hz) 2δCOd/cm-1
νCdO and
LLa
(PPh3)2
dppm
dppe
Ag (71)
OAr (41)
Ag (83)
OR (85)
Ag (88)
OR (85)
Ag (88)
OAr (99)
Ag (90)
Ag (85)
OR (87)
Ag (100)
Ag (76)
7.1 (3697) 166.9 (66, 4) 1675, 1631
-59.7 (3005)
B. Phenoxide Method. The complex (dppm)PtCl2 (251.9 mg,
387.3 µmol), p-NaOC6H4OCH3 (204.9 mg, 1402 µmol, 3.6 equiv), and
NaCl (35 mg) were dissolved/suspended in THF (20 mL) under argon
in a 25 mL screw-capped Erlenmeyer flask. The solution turned bright
yellow, and after 3 h, 31P NMR spectroscopy confirmed that conversion
to (dppm)Pt(OC6H4OCH3)2 (δ -67.8 (JPtP ) 2912 Hz)) was complete.
The solution was filtered through a 3 cm Celite pad in air to remove
the NaCl, and the pad was washed with THF (25 mL to load, 3 × 5
mL washes). Water (250 µL, 36 equiv) was added to the filtrate, and
the solution was immediately bubbled with CO2 for 5 min. The solution
turned tan, and cream-colored solids began to form. The 100 mL flask
containing this mixture was capped under CO2, and the solution was
stirred for 2 h. The solid product was isolated by centrifugation, washed
with Et2O (5 mL), water (1 mL), and Et2O (2 × 5 mL), and vacuum-
dried; crude yield ) 204 mg (82%). Solids insoluble in CH2Cl2 were
still present (presumably NaOH), so the product was dissolved in CH2-
Cl2 (15 mL) and the resulting solution filtered through a 1 cm Celite
pad. Cream-colored (dppm)Pt(CO3) was precipitated from the filtrate
by addition of Et2O (20 mL), isolated by centrifugation, washed with
Et2O (3 × 5 mL), and vacuum-dried. Isolated yield ) 102 mg (41%).
1H NMR (CD2Cl2): δ 7.80 (m, 8 H, Ph), 7.50 (m, 12 H, Ph), 4.63 (t,
JPH ) 11 Hz, JPtH ) 56 Hz, 2 H, PCH2). Anal. Calcd (found) for
C26H22O3P2Pt: C, 48.83 (48.82); H, 3.47 (3.64).
Study of Reaction Intermediates in the (dcpe)Pt Isopropoxide
System. THF (1.955 g, 2.21 mL) was added to (dcpe)PtCl2 (26.8 mg,
39.5 µmol) and sodium isopropoxide (3.2 mg, 39 µmol, 0.99 equiv) in
a screw-capped Erlynmeyer flask under argon in a glovebox and the
reaction mixture stirred. After 1.5 h, one-third of the solution (0.660
g, 13 µmol of Pt) was transferred to a screw-capped 5 mm NMR tube
and examined by 31P NMR spectroscopy at both 1.75 and 16 h. The
solution composition was determined to be about 11% (dcpe)PtCl2 (δ
64.9 (JPtP ) 3539 Hz)), 87% (dcpe)Pt(Cl)(O-i-Pr) (δ 61.5 (JPtP ) 4026
Hz), 52.6 (JPtP ) 2988 Hz), JPP ) 2.7 Hz), and 2% (dcpe)Pt(O-i-Pr)2.
Water (0.3 µL, 17 µmol, 1.3 equiv) was then added and the reaction
monitored vs time by 31P NMR. After 20 min, about 10% of the (dcpe)-
Pt(Cl)(O-i-Pr) complex had hydrolyzed to (dcpe)Pt(Cl)(OH), and after
23 h, the solution composition was determined to be about 7% (dcpe)-
32.8 (3518) 168.4 (60, 4) 1675, 1617
dppp
dppb
-12.0 (3377) 167.6 (61, 4) 1661, 1627
2.4 (3509)
1660, 1624
dtpe
dcpe
31.4 (3518) 168.7 (60, 4) 1687, 1662
58.7 (3429) 169.4 (54, 4) 1652, 1629
dppv
dppz
39.9 (3534) 168.3 (58, 4)
32.9 (3503)
a dppm ) bis(diphenylphosphino)methane, dppe ) 1,2-bis(diphe-
nylphosphino)ethane, dppp ) 1,3-bis(diphenylphosphino)propane, dppb
) 1,4-bis(diphenylphosphino)butane, dtpe ) 1,2-bis(di-p-tolylphos-
phino)ethane, dcpe ) 1,2-bis(dicyclohexylphosphino)ethane, dppv )
cis-1,2-bis(diphenylphosphino)ethene, dppz ) 1,2-bis(diphenylphos-
phino)benzene. b Ag ) Ag2CO3, OR ) NaO-i-Pr, OAr ) NaOC6H4OMe.
c CD2Cl2 solution. d Nujol mull
Typical Isopropoxide Reaction: Synthesis of (dcpe)Pt(CO3).
Sodium chloride (5 mg, to seed crystallization of NaCl, fostering
formation of larger crystals to facilitate filtration) and (dcpe)PtCl2 (1.00
g, 1.45 mmol) were dissolved/suspended in THF (∼60 mL) under argon.
Sodium isopropoxide (0.268 g, 3.27 mmol, 2.25 equiv) was then added
in aliquots over a period of 5-10 min with stirring. After 4 d, a 31P
NMR spectrum of an aliquot showed that the reaction to give (dcpe)-
Pt(O-i-Pr)2 (δ 48.4 (JPtP ) 3315 Hz)) was complete. The reaction
mixture was filtered through a dried, fine frit under slight positive
pressure to give a clear orange solution. Water (130 µL, 7.2 mmol, 5
equiv/Pt) was added and the stirred solution promptly bubbled with
carbon dioxide. Within 1 min, a copious white precipitate formed.
The flask was capped under carbon dioxide and allowed to stir
overnight, after which the precipitate was isolated by centrifugation in
air, washed with ether (3 × 5 mL), and dried under vacuum to give
(dcpe)Pt(CO3) (0.856 g, 87%).
The complexes (dppe)Pt(CO3) and (dppp)Pt(CO3),were prepared by
a similar procedure, formation of the isopropoxide complexes being
complete in 3 h. Details are provided in the Supporting Information.
Typical Phenoxide Reaction: Synthesis of (dppb)Pt(CO3). So-
dium chloride (27 mg) and (dppb)PtCl2 (1.013 g, 1.46 mmol) were
dissolved/suspended in THF (∼60 mL). Sodium p-methoxyphenoxide
(451.8 mg, 3.09 mmol, 2.11 equiv) was added in portions with stirring.
A 31P NMR spectrum taken of the resulting bright yellow solution after
2 h showed complete conversion to (dppb)Pt(OC6H4OMe)2 (δ 3.7, JPtP
) 3488 Hz). The reaction mixture was then filtered through a fine
frit with the aid of Celite. The clear filtrate was treated with water
(140 µL, 5 equiv) and the stirred solution promptly bubbled with carbon
dioxide. The flask was capped under carbon dioxide and allowed to
stir overnight, during which a white precipitate formed. The precipitate
was isolated by centrifugation in air, washed with ether (3 × 10 mL)
and dried under vacuum to give (dppb)Pt(CO3) (0.987 g, 99%).
Synthesis of (dppm)Pt(CO3). A. Ag2CO3 Method. Treatment
of (Ph2PCH2PPh2)PtCl2 (248 mg, 384 µmol) with Ag2CO3 (130 mg,
471 µmol, 1.23 equiv) in wet dichloromethane (40 mL) for 1 h gave
ca. 80-85% conversion to the desired carbonate. By 5 h, decomposi-
tion reactions had set in and workup of the reaction by concentration
and precipitation with hexane yielded a product (189 mg) that contained
only about 15% (dppm)Pt(CO3) (identified by comparison of 31P NMR
data with those of an authentic sample; vide infra). Two other
significant products were present. The major product (ca. 65%)
exhibited the splitting pattern of an AB spin system in the 31P NMR
spectrum (CD2Cl2) at δ 23.0 (JPtP ) 3511 Hz) and 1.8 (JPtP ) 4211
Hz) with JPP ) 29 Hz. The minor product (ca. 20%) also exhibited
the splitting pattern of an AB spin system at δ 25.0 (JPtP ) 3434 Hz)
PtCl2, 3% (dcpe)Pt(Cl)(O-i-Pr), 87% (dcpe)Pt(Cl)(OH) (δ 61.8 (JPtP
3915 Hz), 54.1 (JPtP ) 2970 Hz), JPP ) 2.7 Hz), and 3% (dcpe)Pt-
(OH)2.
)
Additional sodium isopropoxide (2.3 mg, 28 µmol, total 2.05 equiv/
Pt) was added to the remaining two-thirds of the reaction mixture in
the Erlynmeyer flask and the mixture stirred for 24 h. An aliquot (0.602
g, 13 µmol Pt) was then transferred to a screw-capped 5 mm NMR
tube and examined by 31P NMR spectroscopy, showing essentially
complete conversion to (dcpe)Pt(O-i-Pr)2 (δ 48.4 (JPtP ) 3315 Hz)).
Water (0.3 µL, 17 µmol, 1.3 equiv/Pt) was then added and the reaction
monitored vs time by 31P NMR. After 30 min, about 15% of the (dcpe)-
Pt(O-i-Pr)2 complex had hydrolyzed to (dcpe)Pt(O-i-Pr)(OH), and after
24 h, the solution composition was determined to be about 4% (dcpe)-
Pt(O-i-Pr)2, 42% (dcpe)Pt(O-i-Pr)(OH) (δ 52.6 (JPtP ) 3267 Hz), 49.7
(JPtP ) 3301 Hz), JPP ) 1.8 Hz), 45% (dcpe)Pt(OH)2 (δ 53.0 (JPtP
)
3241 Hz)), 6% (dcpe)Pt(Cl)(OH), and 2% (dcpe)PtCl2. (Note: Near-
stoichiometric quantities of water were used in these studies to minimize
the effect of hydrogen-bonding by excess water on the 31P chemical
shifts and on the Pt-P coupling constants.1 Under the conditions used
here, the peak positions and couplings for compounds that could be
observed in both the absence and the presence of water agreed within
5 Hz.)
Reaction of (dppp)Pt(CO3) with (PPN)Cl. The complex (dppp)-
Pt(CO3) (6.2 mg, 9.3 µmol) and [(Ph3P)2N+][Cl-] ((PPN)Cl (22.2 mg,
38.7 µmol, 4.2 equiv; vacuum-dried at 100 °C)) were nearly dissolved
in CD2Cl2 (0.65 mL) in a screw-capped 5 mm NMR tube under argon.
31P NMR spectra taken at both 1.25 and 20 h showed that the solution
composition was approximately 90% (dppp)Pt(CO3) and 10% (dppp)-
PtCl2. Five hours after addition of water (1 µL), a 31P NMR spectrum
showed that the solution composition was now 86% (dppp)Pt(CO3)
and 14% (dppp)PtCl2.
1
and 0.6 (JPtP ) 4304 Hz) with JPP ) 29 Hz. A H NMR spectrum
showed doublets (JPH ) 12 Hz) with shoulders attributed to 195P
satellites for the P-CH2 groups of the unknown products at δ 2.22

5480 Inorganic Chemistry, Vol. 35, No. 19, 1996
Andrews et al.
Reaction of (dppp)PtCl2 with PPh2Bn. The complex (dppp)PtCl2
(9.0 mg, 13.3 µmol) and benzyldiphenylphosphine (PPh2Bn, 6.1 mg,
22.1 µmol, 1.7 equiv) were dissolved in CD2Cl2 in a screw-capped 5
mm NMR tube under argon. 31P NMR spectra taken at both 0.5 and
4 h showed, in addition to free PPh2Bn, that the solution composition
was approximately 25% (dppp)PtCl2 and 75% [(dppp)Pt(PPh2-
Bn)Cl+][Cl-]. (The latter complex was identified by its characteristic
31P NMR spectrum (δ 17.9 (dd, JPP ) 388, 16 Hz, JPtP ) 2409 Hz),
-0.4 (dd, JPP ) 388, 30 Hz, JPtP ) 2268 Hz), -1.9 (dd, JPP ) 30, 16
Table 2. Crystallographic Data for (dppp)Pt(CO3) and
(dppp)Pt(CO3)‚CH2Cl2
a
(dppp)Pt(CO3)
(dppp)Pt(CO3)‚CH2Cl2
formula
fw
space group
a/Å
b/Å
c/Å
â/deg
V/Å3
Z
PtP2O3C28H26
667.56
PtP2O3C28H26‚CH2Cl2
752.50
P21/c (No. 14)
10.362(8)
14.743(6)
19.183(10)
122.69(6)
2466.3(14)
4
P21/c (No. 14)
11.744(2)
15.526(3)
15.866(3)
101.58(1)
2834.1(8)
4
Hz, JPtP ) 3435 Hz)), analogous to that of closely related complexes.11-13
)
After addition of water (5 µL), 31P NMR spectra taken at both 2 and
20 h showed that the solution Pt composition had shifted to 9% (dppp)-
PtCl2 and 91% [(dppp)Pt(PPh2Bn)Cl+][Cl-].
T/K
λ/Å
200
0.710 69
1.798
61.4
0.0781
∼298
0.710 69
1.763
X-ray Crystal Structure Determinations. A. (dppp)Pt(CO3).
Crystals of (dppp)Pt(CO3) were obtained by carefully layering a
dichloromethane solution of the compound with ether to permit slow
diffusion to occur. X-ray diffraction data were obtained with an Enraf-
Nonius CAD-4 diffractometer using graphite-monochromated Mo KR
radiation. The crystal system was monoclinic, and from the systematic
absences, the space group was unambiguously determined to be P21/c.
The cell parameters were obtained by a least-squares fit of sin2 θ values
for 25 reflections in the range 8° < θ < 10°, each of which was
measured at two equivalent positions (one with positive θ and one with
negative θ). Integrated intensities were measured by ω/2θ scans with
an ω-scan width of (1.00 + 0.35 tan θ)°, using varying scan speeds
determined by a prescan. Lorentz, polarization, and absorption
corrections were applied, the last based on ψ scans.14 A partial structure
was found using direct methods.15 All remaining non-hydrogen atoms
were found in successive difference maps after refinements by
difference Fourier methods.16 The positional and isotropic displacement
parameters so obtained were then used as starting input to a full-matrix,
least-squares refinement.17 Atomic positional and anisotropic displace-
ment parameters were varied, together with the scale factor, converging
with ∆/σ < 0.01. The extinction correction was omitted after the
extinction coefficient failed to assume a significant value.18 The
F
calcd/g cm-3
µ/cm-1
R(Fo)b
Rw(Fo)c
55.4
0.0714
0.0586
0.0766
a Numbers given in parentheses in this and subsequent tables are
estimated standard deviations in the least significant digit(s). b R(Fo)
) ∑||Fo| - |Fc||/∑|Fo|. c Rw(Fo) ) (∑w(|Fo| - |Fc|)2/∑w|Fo| )1/2
Table 3. Selected Distances (Å) in (dppp)Pt(CO3)
.
2
w/o DMa
w DMb
w/o DMa
w DMb
Pt-P1
Pt-P2
2.216(5)
2.214(5)
2.226(6)
2.220(5)
C1-O3 1.228(18) 1.290(25)
P1-C2 1.802(16) 1.820(24)
Pt-O1 2.063(11) 2.052(14) P2-C4 1.828(17) 1.826(24)
Pt-O2 2.075(11) 2.066(13) C2-C3 1.561(33) 1.425(33)
C1-O1 1.354(24) 1.341(26) C3-C4 1.554(23) 1.456(40)
C1-O2 1.332(22) 1.313(29)
a Structure without dichloromethane solvate. b Structure with solvate.
Table 4. Selected Angles (deg) in (dppp)Pt(CO3)
2
w/o DMa w DMb
96.0(2)
P1-Pt-O2 101.1(3)
P2-Pt-O1 97.5(4)
O1-Pt-O2 65.3(5)
w/o DMa w DMb
quantity minimized was ∑w||Fo| - |Fc|| with weights w ) 1/σ2(Fo)
and σ2(Fo) ) σcs2 + (0.02Fo)2, where σcs2 is the variance due to counting
statistics. Atomic scattering factors were those as calculated by Cromer
and Waber.19 Anomalous dispersion corrections were included.20
Residual maxima in the final difference Fourier map were (2% near
and relative to the Pt atom. Crystallographic data and selected bond
distances and angles are given in Tables 2-4. Additional crystal-
lographic details are provided in the Supporting Information. An
ORTEP21 drawing is shown in Figure 1 (left).
P1-Pt-P2
95.5(2) O1-C1-O2 112.5(13) 116.6(17)
99.8(4) O1-C1-O3 123.2(17) 120.6(21)
98.3(4) O2-C1-O3 124.3(18) 122.7(20)
66.5(5) Pt-P1-C2 119.6(7) 120.9(8)
P1-Pt-O1 166.4(4) 166.3(4) Pt-P2-C4 119.1(7) 121.4(7)
P2-Pt-O2 162.9(3) 164.7(4) P1-C2-C3 115.5(15) 115.5(20)
Pt-O1-C1 91.1(10) 88.3(12) P2-C4-C3 111.0(12) 114.0(18)
Pt-O2-C1 91.0(10) 88.5(11) C2-C3-C4 110.3(15) 128.2(24)
a Structure without dichloromethane solvate. b Structure with solvate.
B. (dppp)Pt(CO3)‚CH2Cl2. Crystals of (dppp)Pt(CO3)‚CH2Cl2
were obtained in the course of trying to crystallize (dppp)Pt(1,2,4-
butanetriolate).1 After multiple crystallizations from dichloromethane-
ether, the dichloromethane solvate of the carbonate complex was
obtained as determined by the subsequent X-ray structural study. The
crystal system, space group, and cell parameters were obtained as
described above, the last values from 25 reflections in the range 10° <
(11) Oliver, D. L.; Anderson, G. K. Polyhedron 1992, 11, 2415-2420.
(12) Anderson, G. K.; Lumetta, G. J. Inorg. Chem. 1987, 26, 1518-1524.
(13) Davies, J. A.; Hartley, F. R.; Murray, S. G. Inorg. Chem. 1980, 19,
2299-2303.
(14) Fair, C. K. MolEN. An InteractiVe Intelligent System for Crystal
Analysis; Enraf-Nonius: Delft, The Netherlands, 1990.
(15) Gilmore, G. J. MITHRIL. A Computer Program for the Automatic
Solution of Crystal Structures from X-ray Data; Department of
Chemistry, University of Glasgow: Glasgow, Scotland, 1983.
(16) Sheldrick, G. M. SHELX-76: Program for Crystal Structure Deter-
mination; University of Cambridge: Cambridge, England, 1976.
(17) Craven, B. M.; Weber, H. P.; He, X. M. The POP Least-Squares
Refinement Procedure; University of Pittsburgh: Pittsburgh, PA, 1987.
(18) Becker, P. J.; Coppens, P. Acta Crystallogr., Sect. A 1974, 30, 129-
147.
Figure 1. ORTEP drawings (50% probability level) of (dppp)Pt(CO3)
(left) and (dppp)Pt(CO3)‚CH2Cl2 (right). Atom labels for the two
structures are the same.
θ < 15°. Data collection, corrections, and structure refinement were
the same as described above. Residual maxima in the final difference
Fourier map were (1% near and relative to the Pt atom. Crystal-
lographic data and selected bond distances and angles are given in
Tables 2-4. Additional crystallographic details are provided in the
Supporting Information. An ORTEP drawing is shown in Figure 1
(right).
(19) Cromer, D. T.; Waber, J. T. In International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol.
IV, pp 71-147.
(20) Cromer, D. T.; Ibers, J. A. In International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol.
IV, pp 148-151.
(21) Johnson, C. K. ORTEPII. Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.

(Diphosphine)platinum(II) Carbonate Complexes
Inorganic Chemistry, Vol. 35, No. 19, 1996 5481
Results and Discussion
Of the (diphosphine)platinum(II) chlorides treated with silver
carbonate to date, the only ones that have failed to give the
corresponding carbonate in good yield have been (dppm)PtCl2,
((C6F5)2PCH2CH2P(C6F5)2)PtCl2 ((C6F5)2PCH2CH2P(C6F5)2 )
dfppe), and (Me2PCH2CH2PMe2)PtCl2. For dppm, decomposi-
tion of the product carbonate is competitive with its formation.
The two major decomposition products have not been identified,
but both no longer appear to have a chelated dppm ligand since
the 31P chemical shifts are now in the range 0-25 ppm rather
than the ca. -60 ppm region typically observed for chelated
dppm.29 Futhermore, 1H NMR suggests that one of these
Syntheses. (LL)Pt(CO3) complexes have been known for
some time, generally having been prepared either from (LL)-
2,5-7
Pt(O2) and CO2
or from (LL)PtCl2 and Ag2CO3.3-5
Platinum carbonate complexes have also been observed to form
from adventitious “decomposition” reactions of platinum hydride
complexes22,23 or, more recently, from reactions of hydroxide
or oxalate complexes.3,24-26 The (LL)Pt(O2) route to carbonate
complexes did not appear to offer the generality that we needed,
particularly for future studies with other metals. In addition,
the dioxygen complexes require a multistep synthesis from
standard platinum starting materials. The simplicity and
potential generality of the metal chloride + silver carbonate
route to carbonate complexes was appealing, but our initial
attempts to reproduce these preparations led to only slow, partial
conversion to the desired product. We therefore conducted a
detailed study of the synthesis of these complexes, resulting in
both new and improved preparations and a number of new
complexes (Table 1).
products is a platinum hydride complex (δ -1.42 (d (JPH
)
1.3 Hz), JPtH ) 410 Hz)). Details of the reactions involving
the latter chlorides can be found in the Supporting Information.
Prior to solving the problems associated with the silver
carbonate route, we examined the hydrolysis of (LL)Pt-
(alkoxide)2 complexes in the presence of carbon dioxide as a
synthetic method (eq 2). This new technique worked well for
No reaction at all occurs between (dppe)PtCl2 and Ag2CO3
in dichloromethane over a period of 24 h when the reagents
and solvents are rigorously anhydrous. With reagent grade
dichloromethane off the shelf, the reaction went to completion,
but took 3 days. An attempt was made to catalyze the reaction
by the addition of triphenylphosphine, which is known to
displace a chloride ion from (LL)PtCl2 to form [(LL)PtL′Cl]+
species.12,13 Catalysis was indeed observed, but isolation of the
product carbonate was then complicated by solubilization of
the silver chloride byproduct through complexation with the
triphenylphosphine.27 The observation that water enhances the
formation of the above mentioned [(LL)PtL′Cl]+ species (see
Experimental Section) suggested that water might also enhance
the silver carbonate reaction. This led to the discovery that
conversion of (dppe)PtCl2 to (dppe)Pt(CO3) by the action of
silver carbonate is complete in only 3 h at room temperature
when the dichloromethane is saturated with water (eq 1).
(2)
the preparation of (dppp)Pt(CO3) and (dcpe)Pt(CO3), provided
that the solvent employed dissolves the sodium isopropoxide
(e.g., THF) and that the resulting solutions are filtered to remove
the precipitated NaCl before treatment with water and carbon
dioxide. The desired product precipitates out in good yield.
For other phosphines, i.e., dppe and especially dppm, colored
byproducts were often observed in the preparation of the
intermediate isoproxide complexes. This is presumably due to
â-hydrogen elimination reactions to give Pt(0)-derived com-
plexes, as observed for (dppe)Pt(OMe)2.30 Furthermore, similar
problems were observed in attempts to prepare palladium
carbonate complexes.31 The use of alkoxides lacking â-hydro-
gens was therefore investigated. Serious decomposition prob-
lems were encountered with potassium tert-butoxide, even with
(dppp)PtCl2, perhaps due to the high basicity and reduction
potential of tert-butoxide or to the generation of unstable
platinum hydroxide complexes from the tert-butoxide.32,33 The
less basic potassium trimethylsiloxide proved more successful,
but different problems ensued.31,34,35 The most successful
variation on this approach employed phenoxides. The p-
methoxy derivative was chosen to minimize the acidity of the
product phenol on hydrolysis, since such acidity could either
inhibit the hydrolysis or lead to strong hydrogen bonding of
(1)
This route is the preferred method for preparing these
complexes; yields are generally in excess of 80%. Use of
commercially available Ag213CO3 allows preparation of corre-
sponding isotopically labeled complexes, which has facilitated
IR and NMR spectroscopic characterization of the carbonate
ligand. The greatest drawback is the large volume of solvent
often required because of the low solubility of most of the
starting chlorides and product carbonates. This synthetic method
was recently successfully extended to the preparation of the
palladium complexes (dppp)Pd(CO3) and (dcpe)Pd(CO3).28
(22) Robertson, G. B.; Tucker, P. A. Acta Crystallogr. 1983, C39, 858-
860.
(28) Koenig, K. S.; Mandal, S. K. Unpublished results.
(29) Garrou, P. E. Chem. ReV. 1981, 81, 229-266.
(30) Bryndza, H. E.; Calabrese, J. C.; Marsi, M.; Roe, D. C.; Tam, W.;
Bercaw, J. E. J. Am. Chem. Soc. 1986, 108, 4805-4813.
(31) Gould, G. L. Unpublished results.
(23) Davies, J. A.; Eagle, C. T.; Pinkerton, A. A.; Syed, R. Acta Crystallogr.
1987, C43, 1547-1549.
(24) Miyamoto, T. K.; Suzuki, Y.; Ichida, H. Bull. Chem. Soc. Jpn. 1992,
65, 3386-3397.
(25) Porta, F.; Ragaini, F.; Cenini, S.; Sciacovelli, O.; Camporeale, M.
Inorg. Chim. Acta 1990, 173, 229-235.
(32) Ladipo, F. T.; Kooti, M.; Merola, J. S. Inorg. Chem. 1993, 32, 1681-
1688.
(26) Olgemo¨ller, B.; Olgemo¨ller, L.; Beck, W. Chem. Ber. 1981, 114,
2971-2978.
(33) Woerpel, K. A.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 7888-
7889.
(34) Andrews, M. A.; Gould, G. L.; Voss, E. J. Inorg. Chem. 1996, 35,
5740-5742.
(35) Andrews, M. A.; Gould, G. L. Organometallics 1991, 10, 387-389.
(27) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry:
A
ComprehensiVe Text, 3rd ed.; Interscience: New York, 1972; pp
1047-1048.

5482 Inorganic Chemistry, Vol. 35, No. 19, 1996
Andrews et al.
the phenol to the product carbonate.1,36 This route worked well
in the few cases tried and is, in fact, the only method we have
found to prepare pure (dppm)Pt(CO3). Interestingly, reaction
of (dppm)PtCl2 with sodium p-methoxyphenoxide required at
least 3 equiv of phenoxide rather than the expected 2 equiv to
give complete conversion to (dppm)Pt(OAr)2. It is possible that
this is due to deprotonation of the dppm methylene carbon to
give [(Ph2PCHPPh2)Pt(OAr)2]-, which is reprotonated upon
hydrolysis and carboxylation.37
has reported IR data for (Ph3P)2Pt(CO3) complexes derived from
labeled dioxygen containing significant amounts of all three
stable oxygen isotopes (16O, 17O, and 18O).25 The reported band
shifts are inexplicably small, i.e., only 5-10 cm-1. We had
hoped that infrared spectra of the fully-labeled 13C carbonate
complexes prepared in the present work would clarify and
confirm the previous metal carbonate vibrational studies.
Instead, more anomalous findings emerged. First is the
multiplicity of bands observed between 1600 and 1700 cm-1
,
Reaction Intermediates. While this work was in progress,
the synthesis of (Me3P)2Pt(OH)2 from the corresponding dini-
trate complex was reported, along with its reaction with carbon
dioxide to give (Me3P)2Pt(CO3).24 Such hydroxide complexes
are undoubtedly intermediates in our alkoxide-mediated carbon-
ate syntheses as well. Indeed, a number of intermediates and
hydrolysis products can be observed during the reaction of (LL)-
PtCl2 with alkoxide anions and water, including species assigned
to be (LL)Pt(O-i-Pr)(Cl), (LL)Pt(OH)(Cl), (LL)Pt(O-i-Pr)2, (LL)-
Pt(O-i-Pr)(OH), and (LL)Pt(OH)2 on the basis of 31P NMR data
and the systematic variation of solution composition as a
function of reaction stoichiometry and the intentional addition
of water. A representative 31P NMR study is given in the
Experimental Section for the (dcpe)Pt series. A characteristic
feature observed for all the asymmetric (LL)Pt(Cl)(OR) com-
plexes is the accentuated difference between the values of the
two 195Pt-31P coupling constants compared to the values found
for the corresponding symmetrical complexes. Thus JPtP ) 3539
Hz for (dcpe)PtCl2 and 3315 Hz for (dcpe)Pt(O-i-Pr)2, while
(dcpe)Pt(O-i-Pr)(Cl) has JPtP ) 4026 and 2988 Hz.
both in the solid state (Nujol mull and KBr disk) and in solution
(CDCl3): 1675 (vs) and 1631 (m) cm-1 for (Ph3P)2Pt(CO3) and
1644 (sh), 1631 (vs), 1581 (m), and 1570 (m) cm-1 for (Ph3P)2-
Pt(13CO3); see Supporting Information for illustrative spectra.
Only one fundamental carbonate vibrational mode is expected
in this region, namely the CdO stretch.47 The extra band or
bands are plausibly attributed to an overtone of the out-of-plane
carbonate bending mode at 818 (m) cm-1 (2 × 818 ) 1636 ≈
1631 cm-1) whose intensity is enhanced by Fermi resonance
with the CdO stretch (1675 cm-1). More disturbing is the large
isotope shift observed for these bands, as much as 45-50 cm-1
.
This is more than the ca. 37 cm-1 expected for an isolated CdO
oscillator with a vibrational frequency of 1675 cm-1 for the
12Cd16O species. We considered the possibility that these
anomalous results were due to the presence of complexes
containing 18O-labeled species as well as 13C-labeled species,
as this could explain both the large shifts and extra band
multiciplities. This is ruled out by the mass spectrometric
observation of nearly pure 13C16O2 in the direct-inlet decom-
position of the precursor Ag213CO3 and statements from the
supplier that, on the basis of the method of synthesis, the 13C-
labeled silver carbonate should not have significant 18O content.
The asymmetric C-O stretch at ca. 1200 cm-1 also shifts
substantially on isotopic substitution (ca. 15-50 cm-1), but the
complexity and variation of the band shapes in that spectral
area upon isotopic substitution precluded definitive analysis. The
symmetric C-O stretch at ca. 985 cm-1 showed relatively little
shift. Finally, the carbonate out-of-plane bending mode at 818
cm-1 for (Ph3P)2Pt(CO3) shifts 25 cm-1 to 793 cm-1 for the
labeled complex.
NMR Spectral Data. Selected 31P and 13C NMR spectral
data for the carbonate complexes are given in Table 1. The
195Pt-31P coupling constants are intermediate between those
observed for the corresponding dichloride and dialkoxide
complexes. The 13C chemical shifts of these platinum com-
plexes (165-170 ppm), determined here for the first time, fall
in the same range as those previously observed for (ammine)-
CoIII(carbonate) complexes38,39 and for carbonyl phosphine
carbonate complexes of tungsten and ruthenium.40 Coupling
of the carbonate carbon to both 195Pt and 31P is observed (2JPtC
3
≈ 60 Hz, JPC ≈ 4 Hz).
X-ray Structures. Single-crystal X-ray structural studies
have been performed on two different crystalline modifications
of (dppp)Pt(CO3), one with a dichloromethane of solvation and
the other without. Selected bond distances and angles are given
in Tables 3 and 4. Aside from conformational differences
primarily associated with the phenyl groups (see Table S10 of
dihedral angles in Supporting Information), the structures are
nearly identical. The only significant differences in bond
distances and angles involve the center methylene carbon (C3)
of the dppp ligand. From Figure 1 (right) it can be seen that in
the room-temperature, solvated structure this carbon has rather
high displacement amplitudes, leading to shortened bond
distances and a larger C2-C3-C4 bond angle due to fitting of
the banana-shaped electron-density distribution with an el-
lipsoidal function. In the low-temperature structure of the
unsolvated complex (Figure 1, left), these displacements are
lower, yielding more accurate bond distances and angles. In
both structures the Pt-dppp six-membered chelate ring adopts
a flattened-chair cyclohexane form, as commonly observed.1 A
number of apparent C-H‚‚‚O and, in the solvated structure,
C-H‚‚‚Cl weak, intra- and intermolecular hydrogen-bonding
interactions are observed (H‚‚‚O < 2.5 Å and H‚‚‚Cl < 3.2 Å;
see Tables S11 and S12 and descriptive information in the
Supporting Information). The carbonate ligand bond distances
and angles show no statistically significant differences in any
of the total of five (LL)Pt(CO3) complexes that have been
Vibrational Spectra. The vibrational spectroscopy of metal
carbonate complexes, such as [CoIII(NH3)4(CO3)]+, has in
principle been rather well-investigated41-47 and includes two
normal-coordinate analyses.48,49 Surprisingly though, these have
not been confirmed by isotopic labeling. One synthetic study
(36) Kegley, S. E.; Schaverien, C. J.; Freudenberger, J. H.; Bergman, R.
G.; Nolan, S. P.; Hoff, C. D. J. Am. Chem. Soc. 1987, 109, 6563-
6565.
(37) Cf.: Li, J. J. J.; Sharp, P. R. Inorg. Chem. 1994, 33, 183-184 and
references therein.
(38) Massoud, S. S.; Milburn, R. M. Inorg. Chim. Acta 1988, 154, 115-
119.
(39) Woon, T.-C.; O’Connor, J. Aust. J. Chem. 1979, 32, 1661-1667.
(40) Allen, D. L.; Green, M. L. H.; Bandy, J. A. J. Chem. Soc., Dalton
Trans. 1990, 541-549.
(41) Goldsmith, J. A.; Ross, S. D. Spectrochim. Acta 1968, 24A, 993-
998.
(42) Gatehouse, B. M.; Livingstone, S. E.; Nyholm, R. S. J. Chem. Soc.
1958, 3137-3142.
(43) Nakamoto, K.; Fujita, J.; Tanaka, S.; Kobayashi, M. J. Am. Chem.
Soc. 1957, 79, 4904-4908.
(44) Goldsmith, J. A.; Ross, S. D. Spectrochim. Acta 1967, 23A, 1909-
1915.
(45) Greenaway, A. M.; Dasgupta, T. P.; Koshy, K. C.; Sadler, G. G.
Spectrochim. Acta 1986, 42A, 949-954.
(46) Healy, P. C.; White, A. H. Spectrochim. Acta 1973, 29A, 1191-1195.
(47) Elliott, H.; Hathaway, B. J. Spectrochim. Acta 1965, 21, 1047-1054.
(48) Fujita, J.; Martell, A. E.; Nakamoto, K. J. Chem. Phys. 1962, 36, 339-
345.
(49) Hester, R. E.; Grossman, W. E. L. Inorg. Chem. 1966, 5, 1308-1312.

(Diphosphine)platinum(II) Carbonate Complexes
Inorganic Chemistry, Vol. 35, No. 19, 1996 5483
studied by single-crystal X-ray diffraction, namely LL )
(PMe3)2,24 (PEt3)2,23 (P-i-Pr3)2,22 (PPh3)2 (two crystalline
forms),50,51 and dppp (the present work), except for the PMe3
complex, which has a very asymmetric carbonate ligand,
possibly due to hydrogen-bonding interactions with the water
molecules present.24
stretching frequencies, do not change sufficiently as a function
of phosphine to permit systematic correlations with, e.g.,
phosphine basicity57 or diol binding constants.1 Apparently, the
electronic effect of the phosphines is not efficiently transmitted
to the CdO portion of the carbonate ligand. Phosphine basicity
does, however, appear to be linked to the synthetic difficulties
we encountered, the greatest problems occurring with the
electron-deficient dppm and dfppe carbonate complexes. We
believe that this may be due to their higher tendency to undergo
decomposition via ligand-induced loss of carbon dioxide to
generate reactive platinum oxo species as evidenced by the
exchange and phosphine oxidation reactions of (dppp)Pt(CO3)
reported elswhere.34
Conclusions
Platinum carbonate complexes have proven to be useful
synthetic intermediates for the preparation of a wide range of
Pt0,2,52,53 PtII,1,7,54,55 and even PtIV complexes.56 The formation
of volatile byproducts, e.g., CO2 and H2O, in these reactions
makes the isolation of pure products especially easy. The
present work provides significantly increased access to these
generally air-stable carbonate precursors, the improved silver
carbonate route being particularly simple and straightforward
in most cases. The carbonate ligand parameters for these
complexes, e.g., the 13C NMR chemical shifts, 31P-13C and
195Pt-13C NMR coupling constants, CdO distances, and CdO
Acknowledgment. We thank Drs. Morris Bullock and
Thomas Koetzle for helpful discussions and Nicole Brunkan
for some experiments. This research was carried out at
Brookhaven National Laboratory under Contract DE-AC02-
76CH00016 with the U.S. Department of Energy and supported
by its Division of Chemical Sciences, Office of Basic Energy
Sciences. The participation of K.S.K. in this work as a Science
and Engineering Research Student was supported by the U.S.
Department of Energy Office of University and Science Educa-
tion Programs, Office of Energy Research.
(50) Gregg, M. R.; Powell, J.; Sawyer, J. F. Acta Crystallogr. 1988, C44,
43-46.
(51) Cariati, F.; Mason, R.; Robertson, G. B.; Ugo, R. Chem. Commun.
1967, 408.
(52) Blake, D. M.; Leung, L. M. Inorg. Chem. 1972, 11, 2879-2883.
(53) Blake, D. M.; Mersecchi, R. J. Chem. Soc. D 1970, 1045-1046.
(54) Clarke, D. A.; Kemmitt, R. D. W.; Mazid, M. A.; McKenna, P.;
Russell, D. R.; Schilling, M. D.; Sherry, L. J. S. J. Chem. Soc., Dalton
Trans. 1984, 1993-2002.
(55) Eaborn, C.; Metham, T. N.; Pidcock, A. J. Chem. Soc., Dalton Trans.
1975, 2212-2214.
(56) Eaborn, C.; Pidcock, A.; Steele, B. R. J. Chem. Soc., Dalton Trans.
1975, 809-813.
Supporting Information Available: Text giving additional ex-
perimental details, infrared spectra, and tables of crystallographic data,
atomic coordinates, and bond distances and angles (17 pages). Ordering
information is given on any current masthead page.
IC9603159
(57) Sowa, J. R.; Angelici, R. J. Inorg. Chem. 1991, 30, 3534-3537 and
references therein.